Sometimes it's not the anti-virus that is to be blamed. Earlier this year my brother complained that his Lenovo laptop, which has been working perfectly well, was unusable on his wifi network.
Sure enough, I tried it, and cabled LAN was fine, but as soon as wifi was started up, it connected to the LAN, but the machine just bogged down. AVG antivirus was taking all the CPU. Removed AVG, the machine worked fine on the wifi. Tried AVAST, same thing happened, wifi caused the machine to bog down.
So I decided to have a look at exactly what the antivirus was doing using some of the sysinternals (now microsoft) process explorer tools. I found both AV packages were really interested in one html file... It turns out that from the day my brother got his laptop, all his wifi activity was being logged to the debug file (not the raw packet data, but still pretty detailed, and very frequently updated), which Lenovo had decided to give a .html file extension. Any change to that was getting the attention of the AV and forcing it to scan the file. Initially this wasn't an issue as the file was small. By the time I got to investigate, the file was 5meg!
I added the file to the AV exclude list, and weeeee, back up to speed again! A bit of digging found the switch to turn off the wifi debug log in the Lenovo access connections package and I deleted the file.
His machine had been bought new, so why it was set to log by default is beyond me. Why they chose to give the log file a .html extension is also beyond me, as it was raw text.
For my own machines I use a variety - I believe that a mixture is a good thing, if one package misses something bad, and it starts to spread on the network, hopefully one of the other packages will spot it and alert me to its presence. I can then do something about it.
I also add quite a few excludes to the file list, preventing the scanning of source code and txt files.